188 



EOMEGASPIRA. 



is no trace of the baso-axial radial barriers of Megaspira. 

 This diversity between the Eocene and modern groups causes 

 me to separate them generically. See pi. 29, fig. 17, drawn 

 from a specimen in coll. A. N. S. Phila. 



Both Megaspira and Eomegaspira are very highly special- 

 ized. The former, in inheriting the lamellae at an earlier age, 

 gives evidence of the longer life of the group since the 

 acquisition of lamellse. In Eomegaspira the lamellae are ab- 

 sent until nearly the adult stage, but are then enormously 

 developed, their evolution having been too rapid to be yet 

 pushed back to the younger stages through acceleration; and 

 the extinction of the group was probably due to its extreme 

 specialization. Eomegaspira cannot be regarded as in any 

 sense ancestral to Megaspira or to any other known genus. 

 It is the termination of a phylum which diverged from the 

 ancestors of Megaspira and run its course in Cretaceous time, 

 the species known to us straying into the Eocene. In Eng- 

 land a small species existed as late as the Oligocene; but no 

 trace of the genus has oeen found in the rich deposits of that 

 age in central Europe. 



There are two species in the Paris Basin : E. exarata (Mich- 

 aud) and E. elongata (Mellv.). See Deshayes, t. c., pp. 863, 

 864; and Sandberger, Die Land- und Siisswasser- Conchylien 

 der Vorwelt, pp. 156, 172. Cossmann has united them, but 

 I think injudiciously (Ann. Soc. Malac. Belg., xxiv, 1889, p. 

 362). To these are to be added two English species described 

 as Megaspira: E. cylindrica (Edwards MS., Newton) of the 

 London Clay, and E. monodonta (Edw. MS., Newton) from 

 the Oligocene of Headon Hill (see Proc. Malac. Soc. London, 

 i, pp. 73, 74) . Both are small species, known by imperfect 

 single specimens, which however show the characteristic colu- 

 mellar and parietal lamellae. Pupa multispirata Edw. MS., 

 Newton (t. c., p. 72), is probably a cast of the early whorls 

 of Eomegaspira monodonta. Whether these small British 

 species had the palatal armature of the large Parisian forms 

 or not is unknown; but they evidently belong to the same 

 phylum, even though they prove less specialized. 



PI. 29, fig. 17, represents the interior of the last whorl of 



